Twitter has just introduced keyword targeting to their Promoted Tweet program and it’s pretty Sweet.

Instead of inserting ads based on the general interest graph, Twitter can now target individuals who mention a specific keyword. Stack a location choice on top of that and you’ve got a display ad that should convert way more often than your average Promoted Tweet.

Twitter says that one of their beta testers, wearable camera company @GoPro, received almost 2 million impressions with an engagement rate up to 11% using keyword targeting.

What’s not to believe? Responding directly to a person’s needs means there’s a greater chance of follow-through. Send me a lunch coupon in the evening and I’m likely to pass. Send it to me at noon and I’m on my way. Then there’s that added bonus of Twitter’s portability. Of all the social networks, it’s the one that I find easiest to scan on a smartphone while I’m on the go. There’s an immediacy that works.

The only downside is the creep factor. As a marketer, I understand the need for targeting. As a consumer, I actually appreciate seeing ads that are relevant. But I still get a little wigged out when I see ads following me around the internet. Twitter’s keyword targeting goes even further because it’s a response not just a duplication.

Let me see if I can explain that better. I visit CVS.com, look at vitamins, then I leave and go to my favorite entertainment news site. There in the sidebar is an ad for CVS vitamins. I get it. My browser kept track of where I was and reported that to the ad network which sent the ad in hopes that I’ll go back and buy what I was looking at minutes ago.

On Twitter, I type a random comment about feeling tired, maybe I need vitamins. Suddenly, here’s a Tweet from CVS saying, here’s a deal on vitamins. Under the surface, it’s the same mechanism, but to the consumer, it’s like CVS is reading my Tweets and I’m not sure I’m comfortable with that.

Yes, I know my Tweets are public. I often get sales pitches from humans who currently scan for keywords by hand, so it’s not a new concept. It’s still a little creepy. Effective, but creepy.